The home heating oil industry has a long and proud history, and Fuel Oil News has been there supporting it since 1935. It is an industry that has faced many challenges during that time. In its 77th year, Fuel Oil News is doing more than just holding
Issue link: https://read.dmtmag.com/i/693027
44 JULY 2016 | FUEL OIL NEWS | www.fueloilnews.com Example: 4 inch to 8-inch reducer; the reducer ratio is ½ and the smaller pipe diameter is 4 inches. So, from the chart the equivalent would be 7 inches. For our job that means adding 3 feet to the 17½ feet bringing the total TEPL for the water heater to 20½ feet, again well below the chimney design of 22½ feet we have already established for the chimney. We said that we had a 35-foot chimney. We deducted 5 feet for the height of where the flue pipe goes into the chimney leav- ing us an actual chimney height of 30 feet. Seventy-five percent of that leaves us a working dimension for a flue pipe of no more than 22½ feet which is the maximum allowed by both of our NFPA Standards. For any other application you should follow this procedure as outlined by Field Controls in Table 6-4 using a cone or tapered transition piece as shown in Figure 6-7. Okay, that's all out of the way. Now I want to take you through how I would do a multiple unit. I don't go against OEM specifica- tions on a new installation, ever! But, when a job is a few years old and it has been a problem since day one, it's time to try something else. Numbers and good simple math just don't lie. TABLE 6-4 Both of these jobs have 7-inch flue pipe coming out of the breeching of the boilers and we'll do the sizing of the combina- tion flues later. In Figure 6-8 we have another one of those jobs loaded with 90-degree elbows, four to be precise. In Figure 6-9 we have the same job converted to 45-degree elbows. The tees have become Y-Connectors and I just want to focus on those since the pipe lengths and transitions will be just about the same and you know how to figure those now, right? The four 90-degree elbows equal 12 feet each and the two tees are worth 44 feet each for a total of 136 feet of TEPL, and remember that doesn't include the transitions and piping. But, if I switch to four 45-degree elbows at 6 feet each and add the two Y-Connectors at 23 feet each, my new TEPL just for fittings is now 70 feet of TEPL or roughly half of what I began with. By the way, just to vent that 90-degree job without the piping figured in you need a chimney 180 feet high, think about it! At this point it's time to do some sizing of multiple unit flue pipes and wrap this section up. We have so far sized everything but the common vent pipes and taken a look at transitions. What about those transitions, and again there's a right way and a wrong way. In Figure 6-10, courtesy of the fine folks at Tjernlund Products, you can see that there are two types of tran- sitions. The one on the left is wrong and is known as a pancake reducer. The one on the right is correct and is known as a cone or tapered type of reducer as we already showed you in Figure 6-7. Naturally both have the ability to transition up or down and so could also be called increasers. The cone type is the only one we've shown because it's the right one for flue pipes. I don't know where you would use a pancake type, but I would never put one in a flue pipe and I know they make warm air ductwork whistle. The cone type allows the fluegas to easily transition from one size to the next without any additional turbulence added to the fluegas. The pancake reducer will create a lot of problems and can even increase the pressure drop in the flue and create a partial blockage by creating a bullhead tee effect. Let's say that instead of using the cone type we use a pancake type and we are decreasing pipe size with the flow headed into the fitting from large to small. The air (fluegas) will strike the sides of the fitting and curl back onto the air trying to get out and a pressure fight COMMON VENT CAPACITY COMBINED INPUT CAPACITY IN BTU/HOUR Useable Chimney Height 4" 5" 6" 7" 8" 10" 12" 10' 60,000 95,000 135,000 190,000 250,000 395,000 560,000 15' 70,000 115,000 165,000 225,000 305,000 480,000 690,000 20' 80,000 130,000 185,000 260,000 340,000 550,000 790,000 30' 145,000 215,000 300,000 400,000 650,000 940,000 50' 360,000 490,000 810,000 1,190,000 COMMON VENT DIAMETER EQUIVALENT LENGTH IN FEET OF VENT PIPE FOR VENT PIPE FITTING Vent Pipe Fitting d/D 3" 4" 5" 6" 7" 8" ¼ 8 11 14 17 19 22 ½ 5 7 8 10 12 13 ¾ 2 3 3 4 4 5 VENT PIPE DIAMETER Sudden Reducer or Increaser for 3 ratios BOILER BOILER BOILER BOILER BOILER BOILER Figure 6-8 Figure 6-9 TABLE 6-5 Figure 6-7